Light-stable poly-alpha-olefin compositions



2,964,495 LIGHT-STABLE POLY-a-OLEFIN COMPOSITIONS No Drawing. Filed May20, 1959, Ser. No. 814,384

6 Claims. (Cl. 260-45.75)

This invention relates to the stabilization of poly-aolefincompositions. Preferred embodiments of the invention relates to thestabilization of polyethylene and polypropylene compositions againstdeterioration resulting from exposure to sunlight or ultraviolet lightwith a novel synergistic stabilizer combination.

Poly-a-olefins such as polyethylene, polypropylene and the like aresubject to photo-oxidation when exposed to sunlight. This oxidation ischaracterized in its earlier stages by the breaking of the polymer chainand the formation of carbonyl groups. As the oxidation continues, thepolymer cracks and loses tensile strength to the point of mechanicalfailure. A number of so-called ultraviolet inhibitors are known whichinhibit the photodegradation of many polymers, resins or plastics.However, many etfective stabilizers for halogen-containing polymers, forexample, such as polyvinyl chloride, polyvinylidene chloride and thelike are not effective stabilizers in poly-a-olefins as stabilizers inhalogen-containing polymers function essentially as hydrogen halidescavengers while stabilizers in halogen-free poly-a-olefins do not servethis function. Likewise, ultraviolet inhibitors which are eminentlysuited for such cellulosic esters as cellulose triacetate, celluloseacetate butyrate and the like are not necessarily effective ultravioletinhibitors for poly-a-olefins because of the inherently different natureof poly-a-olefins. Hence, it is highly unpredictable as to Whether agiven ultraviolet inhibitor compound will be effective in poly-a-olefincompositions.

' At least as unpredictable is the determination of Whether or not agiven combination of two or more stabilizer compounds will synergize toproduce a stabilizing effect in poly-a-olefins that is greater than theadditive effect of the individual stabilizers. We know of no methodwhereby a combination of stabilizers can be predicted to be synergisticstabilizers for poly-a-olefin compositions short of actually testing thecombination, even though the individual components comprising thecombination may be well-known stabilizers for various polymers, resinsor plastics, including poly-a-olefin compositions.

Apart from the fact that it is an unexpected scientific discovery whentwo stabilizers are found that will synergize with each other in apoly-u-olefin compositions, there are certain practical advantages thatoften times accompany the use of such a combination of stabilizers asdistinguished from the use of a single stabilizer material or compound.For example, one of the stabilizers of the combination might be costlyor difiicult to acquire in commercial amounts while the other stabilizerof the combination might be relatively cheap and readily available. Insuch a situation it would be desirable to be able to substitute thecheaper stabilizer for a portion of the more expensive stabilizer, andstill be able to obtain good stabilization through the synergism of thestabilizer combination. Thus, it is highly desirable in thepoly-a-olefin art to have available synergistic combinations of two ormore materials.

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It is an object of this invention to provide a new synergisticcombination for stabilizing poly-a-olefin compositions.

It is another object of this invention to provide novel polyethylene andpolypropylene compositions containing synergistic combinations ofcompounds that improve the stability of the poly-ethylene andpolypropylene compositions against deterioration resulting from exposureto sunlight or ultraviolet light.

Other objects of the invention will be apparent from the description andclaims that follow.

The present invention comprises poly-a-olefin compositions havingincorporated therein a stabilizing amount of a combination of powderedferric oxide and 2,2'-methylenebis 6-tertiary-butyl-p-cresol).

The ferric oxide (Fe O component of the present combination is in powderform, usually in particles less than 500 millimicrons and preferably inparticles 25 to 350 millimicrons in diameter.

The 2,2'-methylenebis(6-tertiary-butyl-p-cresol) component of thesubject combination is a well known material having the formula (CHa)aCCH CH3 CH When combined with 2,2'-methylenebis(6-tertiarybutyl-p-cresol)the described ferric oxide produces a stabilizing effect inpoly-a-olefins that is greater than the additive or aggregativestabilizing effect of these individual stabilizers. Such combinationsare generally referred to as synergistic combinations. It has been reported in the literature that iron compounds catalyze the breakdown ofsuch plastics as polyvinyl chloride, reference being made to PolymerDegradation Mechanisms, p. 106, (1953), Nat. Bur. of Standards Circular525. Thus, it was unexpected to find that ferric oxide cooperates with2,2-methylenebis(6-tertiary-butyl-p-cresol) to protect poly-ot-olefinsagainst degradation resulting from exposure to ultraviolet light.

The combination of 2,2-methylenebis(6-tertiary-butylp-cresol) and ferricoxide can be used to stabilize a wide variety of poly-a-olefincompositions against deterioration resulting from exposure toultraviolet light. Any of the normally solid polymers of a-monoolefinicaliphatic hydrocarbons containing 2 to 10 carbon atoms can be stabilizedin accordance with the invention. The subject stabilizer combination ispreferably used in polyethyleneand polypropylene, and particularlypolyethylene, although such poly-a-olefins as poly 4-methylpentene-l,poly 3-rnethylbutene-l, poly 3,3-dimethyl-butene-l, poly pentene-l, polydecene-l and the like are included in the invention. Both the so-calledlow density and high density poly-u-olefin compositions can bestabilized in accordance with the invention. Low density polyethylenesusually have densities of .91 to .93, and high density polyethylenesusually have densities of .94 to .97. A typical low densitypolypropylene has a density of .85 and a typical high densitypolypropylene has a density of .92. The densities of otherpoly-u-olefins are known in the art. Reference is made to Fawcett et al.U.S. Patent No. 2,153,553 granted April 11, 1939, and to applicationsCoover U.S. Serial No. 559,536 filed January 17, 1956 and Coover et al.U.S. Serial No. 724,904 filed March 31, 1958, with regard to thepreparation of various poly-a-olefin compositions that can be stabilizedagainst ultraviolet deterioration with the subject stabilizercombination. The subject stabilizer combination can be used as anultraviolet inhibitor for the more common solid resinous poly-u-olefincompositions having average molecular weights of at. least 15,000 andmore usually at least 20,000, as well as the so-called POIY-ot-OlBfiHwaxes having lower molecular weights, usually 3,000l2,000.

The amount of the combination of the subject 2,2-methylenebis(6-tertiary-butyl-p-cresol) and ferric oxide employed inpoly-a-olefin compositions in accordance with the invention can bewidely varied, the stabilizing amount of this combination usuallyvarying with the particular use to which the poly-a-olcfin is to be put.Concentrations of the combination of at least .001% are generally used,and concentrations of .l% to 10% are preferably used, the concentrationbeing based on the weight of the poly-a-olefin. The weight ratios of thestabilizers comprising the subject synergistic combination likewise canbe varied. We prefer to utilize the combination of the subjectstabilizers at weight ratios of2,2'-methylenebis(6-tertiary-butyl-p-cresol) to ferric oxide rangingfrom l/30 to 30/1, with ratios of 1/30 to l/1 utilizing higherproportions of ferric oxide being preferred.

The stabilizer combination of the invention can be incorporated orblended into poly-ot-olefin compositions by conventional methods usedfor blending such materials into resins or plastics. Typical of suchmethods that can be suitably employed include milling on heated rollsand dry-blending. The stabilizers of the invention can be incorporatedseparately or together into the poly-aolefin composition.

The stabilizer combination of the present invention lends topoly-m-olefin compositions improved stability, and more specifically,improved stability against deterioration resulting from exposure tosunlight or ultraviolet light. Thus, poly-a-olefins stabilized inaccordance with the invention have an extended life expectancy and canbe used more effectively than unstabilized poly-ot-olefins for a Widediversity of uses, including outdoor uses requiring prolonged exposureto the elements. Poly-aolefins stabilized in accordance with theinvention can be cast, extruded, rolled or molded into sheets, rods,tubes, piping, filaments and other shaped articles, including the widelyused films of the polymer about .5 to 100 mils in thickness. Thepresentcompositions can be used for coating paper, wire, metal foil,glass fiber fabrics, synthetic and natural textiles and other suchmaterials. Likewise, small amounts of other additives such as otherpolymers, resins or plastics, as well as other stabilizers orinhibitors, that are commonly added to poly-ot-olefins for specific usesare not deleterious to the effectiveness of the present synergisticcombination.

The invention is illustrated by the following examples of preferredembodiments thereof.

EXAMPLE 1 Into several portion of polyethylene having an averagemolecular weight of about 30,000 and a density of .918 washot-roll-compounded 5% by weight of powdered ferric oxide having aparticle size of 60 millimicrons (Mapico Red 297, Columbian Carbon Co.)plus .S% by Weight of 2,2'-methylenebis(6-tertiary-butyl-pcresol), aswell as these two materials individually and a control containing noadditive. For comparative purposes, portions of the polyethylene wereprepared containing 5% by weight of powdered rutile having a particlesize of 300 milimicrons (Titanox RA-lO, Titanium Pigment Corp.) plus 5%by weight of 2,2-methylenebis(6- tertiary-butyl-p-cresol), as well asthese two materials individually. The resulting polyethylenecompositions were thereafter compression-molded into sheets 125 mils inthickness, 10 samples 1.5 x .5 inch in size diced out of the compressionmolded sheets for each polyethylene composition, the resulting samplesbent into a U-shape and then exposed to outdoor weathering at Kingsport,

Tennessee. The stressed portion of each sample was mounted facing south.The exposure times in days required to start cracks in half of thesamples (5 samples for each polyethylene compoistion) are summarizedbelow in Table A. In Table B below is summarized the appearance of therespective samples after are exposure of 2 years.

Table B Additive Appearance After 2 Years of Exposure (1) None Broken atend of first year. (2) 5% Ferric Oxide Fine cracks, dull surface. (3).5% 2,2 Methylcnebis(6-tert;.-butyl- Broken.

p-cres (4) 5% Rutile Deep, wide cracks, dull surface. (5) 5% Rutile+.5%2,2-Methylenebis (6- Fine cracks, shiny surface.

tert.-butyl-p-cresol). (6) 5% Ferric Oxide+.5% 2,2-Mcthy1-enebis(6-tert.-butyl-p-cresol) Shiny, uncracked surface.

As can be observed from the comparisons set out in the above tables,particularly the quantative comparative data set out in Table A, thecombination of ferric oxide and2,2'-methylenebis(6-tertiary-butyl-p-cresol) has a stabilizing effect inpolyethylene that is substantially greater than the additive effectiveof the individual components of this combination. Rutile, which isessentially titanium dioxide and is a conventional pigment material,does not synergize like ferric oxide with2,2'-methylenebis(o-tertiary-butyl-pcresol) in the subject poly-a-olefincomposition.

EXAMPLE 2 A .5 by weight portion of 2,2-rnethylenebis(6-tertiary-butyl-p-cresol) in combination with a 5% by weight portion ofpowdered ferric oxide as described in Example 1 incorporated intopolypropylene having an average molecular weight of 110,000 and adensity of .917, when prepared in test samples and exposed to weatheringas described in Example 1, show a synergistic effect in stabilizing thepolypropylene against deterioration resulting from the exposure.

The present invention thus provides novel pcly-a-olefin compositionshaving improved stability against deterioration resulting from exposureto ultraviolet light, and particularly it provides novel and usefulsynergistic stabilizer combinations for poly-u-olefin compositions.

Although the invention has been described in detail with reference topreferred embodiments thereof, it will be understood that variations andmodifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined by the appendedclaims.

We claim:

1. A solid poly-a-olefin composition comprising a poly-a-olefin preparedfrom an a-monoolefinic aliphatic hydrocarbon having 2 to 3 carbon atomscontaining at least 001% by weight based onsaid poly-e-olefin of astabilizer combination comprising 2,2 -rnethylenebis(6-tertiary-butyl-p-cresol) and powdered ferric oxide.

2. A solid poly-a-olefin composition comprising a polya-olefin selectedfrom the group consisting of polyethylene and polypropylene containing.l% to 10% by weight based on said poly-a-olefin of a stabilizercombination comprising 2,2 methylenebis(6 tertiary butyl pcresol) andpowdered ferric oxide, the weight ratio of said2,2-methylenebis(6-tertiary-butyl-p-cresol) to said ferric oxide beingin the range of 1/ 30 to 30/ 1.

3. A solid poly-a-olefin composition comprising polyethylene containing.1% to 10% by weight based on said polyethylene of a stabilizercombination comprising 2,2- methylenebis(6-tertiary-butyl-p-cresol) andferric oxide in the form of particles 25 to 350 millimicrons in size,the weight ratio of said 2,2'-methylenebis(6-tertiary-butylp-cresol) tosaid ferric oxide being in the range of 1/ 30 to 1/1.

4. A solid poly-aolefin composition comprising polypropylene containing.1% to 10% by weight based on said polypropylene of a stabilizercombination comprising 2,2-methylenebis(6-tertiary-butyl-p-cresol) andferric oxide in the form of particles 25 to 350 millimicrons in size,the weight ratio of said 2,2'-methylenebis(6-tertiarybutyl-p-cresol) tosaid ferric oxide being in the range of 1/30 to U1.

5. A solid poly-a-olefin composition comprising polyethylene having anaverage molecular weight of at least 15,000 containing about .5% byweight based on said polyethylene of 2,2 methylenebis(6 tertiarybutylp-cresol) and about 5% by weight based on said polyethylene offerric oxide in the form of particles about 60 millimicrons in size.

6. A solid poly-u-olefin composition comprising polypropylene having anaverage molecular weight of at least 15,000 containing about .5% byweight based on said polypropylene of 2,2 methylenebis(6 tertiarybutylp-cresol) and about 5% by weight based on said polypropylene offerric oxide in the form of particles about 60 millimicrons in size.

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain July 2, 1958

1. A SOLID POLY-A-OLEFIN COMPOSITION COMPRISING A POLY-A-OLEFIN PREPAREDFROM AN A-MONOOLEFINIC ALIPHATIC HYDROCARBON HAVING 2 TO 3 CARBON ATOMSCONTAINING AT LEAST .001% BY WEIGHT BASED ON SAID POLY-A-OLEFIN OF ASTABILIZER COMBINATION COMPRISING2,2''-METHYLENEBIS(6TERTIARY-BUTYL-P-CRESOL) AND POWDER FERRIC OXIDE.